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Modem-HOWTO
David S.Lawyer
mailto:dave@lafn.org
v0.38, June 2005
Help with selecting, connecting, configuring, trouble-shooting, and understanding analog modems for a PC.
1. Introduction
- 1.1 DSL, Cable, and ISDN Modems in other HOWTOs
- 1.2 Also not well covered: PCMCIA Modems, PPP
- 1.3 Copyright, Disclaimer, Trademarks, & Credits
- 1.4 Contacting the Author
- 1.5 New Versions of this HOWTO
- 1.6 New in Recent Versions
- 1.7 What is a Modem ?
- 1.8 Does My Computer Contain an Internal Modem ?
- 1.9 Quick Install
- 1.10 dev/modem
2. Modems for a Linux PC
- 2.1 Many Winmodems Will Not Work with Linux
- 2.2 External vs. Internal
- 2.3 Is a Driver Needed ?
- 2.4 External Modems
- 2.5 Internal Modems
- 2.6 Software-based Modems (winmodems, linmodems)
- 2.7 PCI Modems
- 2.8 AMR Modems
- 2.9 USB Modems
- 2.10 Which Internal Modems might not work with Linux
3. Modem Pools, RAS
4. Serial Port and Modem Basics
- 4.1 Modem Converts Digital to Analog (and conversely)
- 4.2 What is a Serial Port ?
- 4.3 IO Address & IRQ
- 4.4 Names: ttyS0, ttyS1, etc.
- 4.5 Interrupts
- 4.6 Data Compression (by the Modem)
- 4.7 Error Correction
- 4.8 Data Flow (Speeds)
- 4.9 Flow Control
- 4.10 Data Flow Path; Buffers
- 4.11 Modem Commands
- 4.12 Serial Driver Module
5. Configuring Overview
6. Locating the Serial Port: IO address, IRQs
- 6.1 What Bus is my Serial Port On?
- 6.2 IO & IRQ Overview
- 6.3 PCI Bus Support
- 6.4 Common mistakes made re low-level configuring
- 6.5 IRQ & IO Address Must be Correct
- 6.6 What is the IO Address and IRQ per the driver ?
- 6.7 What is the IO Address & IRQ of my Serial Port Hardware?
- 6.8 Choosing Serial IRQs
- 6.9 Choosing Addresses --Video card conflict with ttyS3
- 6.10 Set IO Address & IRQ in the hardware (mostly for PnP)
- 6.11 Giving the IRQ and IO Address to Setserial
7. Configuring the Serial Driver (high-level) "stty"
- 7.1 Introduction
- 7.2 Hardware flow control (RTS/CTS)
- 7.3 Speed Settings
- 7.4 Ignore CD Setting: clocal
- 7.5 What is stty ?
8. Modem Configuration (excluding serial port)
- 8.1 Finding Your Modem
- 8.2 AT Commands
- 8.3 Init Strings: Saving and Recalling
- 8.4 Other AT Modem Commands
- 8.5 Blacklisting
- 8.6 What AT Commands are Now Set in my Modem?
- 8.7 Modem States (or Modes)
9. Serial Port Devices /dev/ttyS4, (or /dev/ttys/4) etc.
- 9.1 Serial Port Names: ttyS4, tts/2, etc.
- 9.2 The PCI Bus
- 9.3 Devfs (The Device File System)
- 9.4 Legacy Serial Port Device Names & Numbers
- 9.5 More on Serial Port Names
- 9.6 USB (Universal Serial Bus) Serial Ports
- 9.7 Link ttySN to /dev/modem
- 9.8 cua Device Obsolete
10. Interesting Programs You Should Know About
11. Trying Out Your Modem (Dialing Out)
- 11.1 Are You Ready to Dial Out ?
- 11.2 Dialing Out with wvdial
- 11.3 Dialing Out with Minicom
- 11.4 Dialing Out with Kermit
12. Dial-In
- 12.1 Dial-In Overview
- 12.2 What Happens when Someone Dials In ?
- 12.3 56k Doesn't Work for Dialin
- 12.4 Getty
- 12.5 Why "Manual" Answer is Best
- 12.6 Dialing Out while Waiting for an Incoming Call
- 12.7 Ending a Dial-in Call
- 12.8 Dial-in Modem Configuration
- 12.9 Callback
- 12.10 Distinctive Ring
- 12.11 Voice Mail
- 12.12 Simple Manual Dial-In
- 12.13 Complex GUI Dial-In, VNC
- 12.14 Interoperability with MS Windows
13. Uugetty for Dial-In (from the old Serial-HOWTO)
14. What Speed Should I Use with My Modem?
- 14.1 Speed and Data Compression
- 14.2 Where do I Set Speed ?
- 14.3 Can't Set a High Enough Speed
- 14.4 Speed Table
15. Communications Programs And Utilities
16. Two Modems (Modem Doubling)
17. ISDN "Modems"
18. Troubleshooting
- 18.1 My Modem is Physically There but Can't be Found
- 18.2 "Modem is busy"
- 18.3 "You are already online! Hang up first." (from minicom)
- 18.4 I can't get near 56k on my 56k modem
- 18.5 Uploading (downloading) files is broken/slow
- 18.6 For Dial-in I Keep Getting "line NNN of inittab invalid"
- 18.7 I Keep Getting: ``Id "S4" respawning too fast: disabled for 5 minutes''
- 18.8 Dial-in: When remote user hangs up, getty doesn't respawn
- 18.9 NO DIALTONE
- 18.10 NO CARRIER
- 18.11 uugetty Still Doesn't Work
- 18.12 (The following subsections are in both the Serial and Modem HOWTOs)
- 18.13 Serial Port Can't be Found
- 18.14 Linux Creates an Interrupt Conflict (your PC has an ISA slot)
- 18.15 Extremely Slow: Text appears on the screen slowly after long delays
- 18.16 Somewhat Slow: I expected it to be a few times faster
- 18.17 The Startup Screen Shows Wrong IRQs for the Serial Ports.
- 18.18 "Cannot open /dev/ttyS?: Permission denied"
- 18.19 "Cannot open /dev/ttyS?"
- 18.20 "Operation not supported by device" for ttyS?
- 18.21 "Cannot create lockfile. Sorry"
- 18.22 "Device /dev/ttyS? is locked."
- 18.23 "/dev/tty? Device or resource busy"
- 18.24 "Input/output error" from setserial, stty, pppd, etc.
- 18.25 "LSR safety check engaged"
- 18.26 Overrun errors on serial port
- 18.27 Modem doesn't pick up incoming calls
- 18.28 Port gets characters only sporadically
- 18.29 Troubleshooting Tools
19. Flash Upgrades
20. Other Sources of Information
21. Appendix A: How Analog Modems Work (technical) (unfinished)
- 21.1 Modulation Details
- 21.2 56k Modems (V.90, V.92)
- 21.3 Full Duplex on One Circuit
- 21.4 Echo Cancellation
22. Appendix B: Analog Voice Infeasible Over Non-Voice Modem
23. Appendix C: "baud" vs. "bps"
24. Appendix D: Terminal Server Connection
25. Appendix E: Cable and DSL modems
26. Appendix F: Connecting 2 Modems Directly Back-to-Back (Leased Lines).
27. Appendix G: Fax pixels (dots)
28. Appendix H: Stty Hanging Problem (prior to 2000)
29. Appendix G: Antique Modems
- 29.1 Introduction
- 29.2 Old CCITT (ITU) and Bell Protocols
- 29.3 Historical Overview
- 29.4 Proprietary protocols, etc.
- 29.5 Autobauding
- 29.6 Modem-to-modem Speed
- 29.7 Modem-to-serial_port Speed
- 29.8 Before AT Commands
- 29.9 Acoustic-Coupling
- 29.10 Data Compression and Error Correction
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